As an example of a wireless power transmission system, the electric-field-coupling-scheme wireless power transmission system described in Patent Document 1 is known. In this system, an active electrode and a passive electrode of a power transmission device and an active electrode and a passive electrode of a power reception device are brought close to each other with a gap therebetween, whereby the pairs of electrodes become capacitively coupled with each other and power is transmitted from the power transmission device to the power reception device. In Patent Document 1, in each of the power transmission device and the power reception device, a configuration is adopted in which the active electrode is surrounded by the passive electrode and the coupling capacitance between the passive electrodes is made large. Thus, the tolerance with respect to discrepancies between the relative positions of the power transmission device and the power reception device is high and therefore convenience is high. Along with it being possible to realize a high degree of coupling between the power transmission device and the power reception device and make the power transmission efficiency high, size reduction of the devices is also achieved. A central conductor is electrostatically shielded by a structure that surrounds the central conductor with a peripheral conductor and thereby extraneous emissions can be reduced.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2012-530481
As described in Patent Document 1, in an electric-field-coupling-scheme power transmission system, it is necessary to optimize a coupling capacitance and a coupling coefficient between electrodes in order to make the power transmission efficiency high. In addition, when considering compatibility between many devices, it is necessary to quantify a capacitive coupling unit. However, in the configuration described in Patent Document 1, although the capacitance generated between the electrodes can be made large, the coupling capacitance and coupling coefficient are not known and suitable values for these parameters are not known. Consequently, it is necessary to repeatedly design the active electrodes and the passive electrodes using a so-called “cut and try” process and therefore labor and time are needed.
In addition, in power transmission systems, to date, because the values of coupling capacitances are very small, when a coupling unit has been directly measured, parasitic capacitances generated between the coupling unit and, for example, the probe of a measurement instrument have had an effect and measurement errors have sometimes become large. Consequently, in order to derive the necessary parameters, the necessary parameters have been measured in a state where a transformer unit and the coupling unit are isolated from each other, but in this case there is a problem in that errors are generated in the derived parameters and as a result power transmission cannot be performed with an optimum power transmission efficiency with the final devices that have the transformer units and the coupling unit incorporated therein.